The present invention relates to an apparatus for heating plastic containers, in particular plastic parisons. It is known from the prior art that so-called plastic parisons, in particular made of PET, are initially heated in a kiln and then in the context of a blow moulding process, in particular a stretch blow moulding process, are transformed or expanded into plastic containers with a desired final form. Infrared radiators are often employed as heating elements.
In order to increase the efficiency of heating by the radiation used, the use of reflectors is known from the prior art. For this purpose these reflectors are disposed in such a way that they reflect radiation which is not travelling towards the plastic parison in the direction of the plastic parison to be heated. By means of the use of reflectors it is not only possible to increase the overall efficiency of the heating apparatus, but also to be able to differentiate more precisely in a targeted manner between individual regions of the plastic parison with regard to the required temperature regulation.
For the subsequent successful and efficient progress of the stretch blow-moulding process it may be very important in the heating apparatus to apply increased radiation in a targeted manner to individual regions of the plastic parison, but attenuated radiation is merely applied to other regions. Thus for example the plastic parisons conventionally have a mouth region which is open at the top, is usually formed as an external thread and already in the course of the production of the plastic parisons acquires the shape of the mouth region of the finished container. Thus precisely this region should not be expanded and thereby deformed during the blow moulding process. For this purpose it is necessary as far as possible to omit the mouth region of the plastic parison from the application of radiation in the heating system.
Reflectors are known from the prior art in which the radiation emitted by the heating elements can be focused by the specific curvature of the reflecting surface of the reflectors. A heating system for heating parisons is known from DE 10 2010 049 136 A1, in which a back reflector is provided which has an exposed area or groove in order to be able to be disposed as close as possible to the IR radiator. A lamp device for heating parisons for the production of containers, which device has a reflector curved in the shape of an arc of a circle, is known from EP 2 110 225 A1. Moreover, coated radiation sources are known.
From an as yet unpublished patent application a heating system is known which has a reflector device with a first section with a substantially parabolically curved configuration and a second section with a curved configuration of which the curvature differs from the curvature of the first section.
Moreover, lens radiators or parabolic radiators are known, of which the glass tubes with a circular or elliptical cross-section are modified in such a way that a large part of their inner shell surface is provided with a reflective coating.
From the prior art it has been shown disadvantageously that separately installed reflectors, which are therefore distanced from the radiation source, require a large installation space due to their great distance from the radiation source and the large installation width which is necessary as a result. On the other hand, coated radiators always have a round cross-section. The object of the present invention therefore is to design a heating system for a plastic parison by which a reduction of the installation space is achieved.